1. Field of the Invention
The subject invention relates to soldering and integrated circuit technology, and particularly to apparatus for remelting solder and removing an installed integrated circuit.
2. Description of the Prior Art
Elegant applications of soldering technology have proliferated with the advent of modern electronics. Although the art of joining metals by soldering is centuries old, a deep scientific understanding of the metallurgy and the many different ways of introducing heat to the joint are relatively modern. Electronic components have advanced from components with two leads, like resistors and capacitors, to integrated circuits with 10 to 100 or more leads. The leads on integrated circuits typically emerge from the body of the IC from two or four of the sides of the device. On a "through-hole" device, the leads come out the sides and then bend downward with sufficient length that they project beyond the bottom of the device so that they may pass through holes in printed circuit boards. On a "gull-wing" device, the leads effectively project outward and away from the sides. The leads are formed in such a way that they will come in contact with the top surface of a printed circuit board for surface mounting. On a "J-lead" device, the leads come out the sides, bend down the sides and then may tuck under the bottom of the device. These, too, are surface-mounted devices.
Each of the leads of an IC needs to be soldered to a printed circuit board or otherwise connected to other electronic parts to become a useful part of a system. This joining process may be handled one joint at a time with a small diameter soldering iron, or some means of soldering more than one lead at a time may be devised. Mass joining processes such as wave soldering, infrared radiant soldering, and vapor phase soldering have been developed to reduce assembly time.
A problem occurs, however, when an integrated circuit fails. A failed circuit must be removed and replaced without causing damage to the neighboring parts. Removal of ICs having leads on only two sides is relatively easy. However, it becomes increasingly difficult with four-sided integrated circuits, sometimes referred to as "quad packs." Successful removal of quad packs requires that all of the leads be heated simultaneously until all of the solder becomes liquid. The mass joining processes of wave soldering, infrared radiant soldering, and vapor phase soldering have not adapted well to circuit removal, because it is desired to remelt the leads on only one component, the integrated circuit (IC), while not remelting the other solder joints of other components on an assembly.
The task of removing a single IC while leaving other components undisturbed, has been accomplished by producing localized heat via streams of focused hot gas, typically air, and by specially-shaped soldering iron tips which make contact with the appropriate surfaces of the IC and the printed circuit board (PCB). Hot gas can successfully be applied in the removal of through-hole, gull-wing, and J-lead devices, but it is often criticized because there is spillover of the hot gas to nearby components, which is deemed undesirable. Shaped soldering iron tips have been successfully used for removal of through-hole and gull-wing devices because they can readily make contact with the device leads and the PCB pads. They have not been noted for success in removing J-leaded devices due to poor thermal contact
A heated, nonmoving collet has also been devised which can be made to properly fit gull-wing devices An integral vacuum probe can be used to lift gull-wing devices after the solder is melted if there are no other restraints such as glue or conformal coating.